feat: Extend existing sharedfiles implementation

[3urobeat]

Hi,
this PR extends the existing sharedfiles implementation to...:

• detect workshop item objects as type
• scrape categories
• scrape tags
• implement functions to un-/subscribe from/to workshop items
• rename object methods for un-/subscribing from/to comments to separate them more clearly

Workshop Items are also listed as sharedfiles on the SteamCommunity (see the CS2 Insertion2 map for example), which is why I added support to the existing sharedfiles class, instead of adding a new one.

This PR might display conflicts later on as it is based on the master branch and not on the fixes of my two other sharedfiles PRs (#315 & #316). I'll address them gladly when it is time.

Thanks!

[3urobeat]

Added a patch (to this very stale PR, please review :( ) that fixes getSteamSharedFile() failing to check if account up-/downvoted a greenlight item.

Greenlight items are workshop items that can be voted into a game, e.g. CS skins. These items use a different container to list the voting buttons, hence causing the previous implementation to fail.